siveshen :
display types are not really a factor when it comes to power consumption in a pc though i suspect that vga could use slightly more power than Dvi and possibly Hdmi will use less power than Dvi.
VGA will use A LOT more power than DVI/HDMI since AD/DA converters are inherently highly inefficient: a bunch of resistor or current source networks and analog amplifiers. A digital link uses a few hundred milliwatts while an analog one will use two or three watts, that's a factor of about 10X.
DVI and HDMI use exactly the same video signaling format, which means no meaningful difference beyond connector parasitics.
Compared to the 10-15W used by the GPU to simply scan the VRAM to refresh monitors though, the 300mW or so on digital links...